Traction motors are commonly used in electrically powered rail vehicles such as diesel electric locomotives. Many locomotives today employ a plurality of DC traction motors, typically four or six, to provide sufficient towing power for hauling large payloads over long distances. In some cases, motors are connected in series or parallel, so that they can operate from a common electrical bus, simplifying wiring and electric control of the motors.
In some traction motor systems, the traction motors are hardwired in parallel and/or series with at least three to five other motors. Although this arrangement allows for the motors to share a common electrical bus, it may be susceptible to large scale drive system failure. In these arrangements, a failure of one of the motors in the same circuit may render all motors inoperable. For example, for motors connected in parallel, an electric failure that leads to a short circuit condition in one of the motors may disable all of the other traction motors in the circuit. In such a case, if all of the traction motors for the locomotive reside on the same circuit, the locomotive may lose all driving capability. Thus, to prevent a situation in which the loss of one motor disables the entire locomotive, a system for selectively isolating drive components that experience electrical failures may be required.
One solution for maintaining the traction motor system functionality in the event of a traction motor component failure is described in U.S. Pat. No. 6,497,182 B2 (“the '182 patent”). The '182 patent is directed to a system that purportedly incorporates a brake motor isolation switch disposed in signal communication with at least one of the traction motors for electrically isolating a faulting motor from the other traction motors.
The motor isolation solution provided by the system disclosed in the '182 patent is limited to traction motors in which the armature and the field winding circuit of the motor are connected in series. As a result, any failure that results in tripping of the isolation switch effectively removes both the armature and the corresponding field coil of the motor from the circuit. In certain situations, however, it may be advantageous to retain the ability to selectively remove only the failed component of the motor, rather than the entire motor. For example, in situations where a field winding of the motor has failed, it may be advantageous to allow the armature to remain in the circuit so that the dynamic braking capabilities of the armature are retained. While the '182 patent allows for a traction motor system to isolate a failed motor and to retain the functionality of the remaining motors, it may unnecessarily remove properly functioning components from the system—components that may otherwise contribute to the functionality of the drive system.
The presently disclosed traction motor drive system is directed to overcoming one or more of the problems set forth above and/or other problems in the art.